Question

A person needs a lens of power –4.5 D for correction of her vision.

1. What kind of defect in vision is she suffering from?
2. What is the focal length of the corrective lens?
3. What is the nature of the corrective lens?

Answer 1

1. The negative power of the lens suggests that she must be suffering from myopia.
2. Power, P = ─4.5 D, focal length, f = ?
   
   Now, P = 1/ f
   
   ⟹ f = 1/ P = 1/ −4.5 = −0.222 m = − 22.2 cm
3. Myopia is corrected using a concave or divergent lens.